1. Field of the Invention
The invention relates to a process and a device for detoxifying the waste gases from waste incinerating plants, in particular hazardous waste incinerating plants to eliminate toxic compounds such as organic halogen substances and hydrocarbons.
The invention is particularly provided for the complete elimination of dioxins, CFCs and other toxic substances from the waste gases of waste incinerating plants, in particular hazardous waste incinerating plants.
2. Description of the Prior Art
In addition to the waste dumps which can only be extended to a limited degree for space and acceptance reasons, waste incinerating plants represent practically the one and only problem solution for the elimination of existing waste products for the disposal of industrial and communal waste products, the operating of waste and hazardous waste incinerating plants or the construction of new plants also meeting with increasing resistance and decreasing acceptance. This is particularly attributable to the fact that, as was shown by more recent investigations, the waste gas purification of the waste incinerating plants is insufficient particularly in view of dioxins and other toxic chemical compounds.
The problem consists above all in that bonded chlorine is present in all industrial and communal waste products to a certain degree, which causes the formation of the highly toxic and especially feared higher chlorinated hydrocarbons, in particular dibenzodioxins and dibenzofurans, during combustion.
Considering this problem which has already been known for quite some time, the combustion temperature is bindingly fixed at values above 1200.degree. C. for the greatest possible avoidance or reduction of the formation of such compounds in the flue gas of the waste incinerating plant, this temperature being customarily achieved in the waste incinerating plants mostly by a high-temperature combustion stage connected downstream of the conventionally used rotary tubular kiln.
Nevertheless, it became apparent that emissions of dangerous substances occur in almost all waste incinerating plants despite this, which have a number of causes. These causes consist e.g. in that the combustion chambers in the rotary tubular kilns or in the high-temperature post-combustion allow temperature fields which are inhomogeneous in terms of space and time to occur in their interior due to heat surges at different points. In addition to this, the heterogeneity of the supplied waste products, e.g. as regards calorific values, composition, etc., requires a complex control of the undergrate firing performance or the batch combination in order to observe the required minimum temperatures.
Moreover, it was detected more recently that dioxins can also be formed at lower temperatures, e.g. in the range of 300.degree. to 400.degree. C. as they prevail in and downstream of the waste heat boiler of the incinerating plant, at a later point in time and independently of the high-temperature incinerating stage in the case of the presence of hydrocarbon residues from the combustion, chlorine-containing compounds and oxygen and in the presence of catalytically acting dusts.
Above all, not decomposed organic chloride substances from the combustion and the high-temperature combustion stage, and newly formed organic chloride substances from residual hydrocarbons not decomposed by the high-temperature combustion in the area of the waste heat boiler at temperatures between 300.degree. and 400.degree. C., are thus emission sources for hazardous products.
Since these disadvantages are in general inherent to hazardous waste incinerating plants (destruction efficiency for chlorinated hydrocarbons being 99.998% as a maximum) their ecopolitical acceptance is already basically questioned without alternative concepts for a waste product elimination without the use of incinerating plants having been actually made available so far.
Due to the waste eliminating capacity of such plants which, on the other hand, is high, efforts must above all be focussed on a waste gas atmosphere from waste incinerating plants, which is actually completely free from residues of highly toxic compounds.
It has already been attempted to bypass the new formation of polychlorinated hydrocarbons by the fact that the temperature range of from 400.degree. to 300.degree. C. is rapidly traversed by means of the injection of water. However, this solution has the disadvantage that the formation of dioxins and furans cannot be safely and reliably prevented. Moreover, the pre-formed dioxins and furans and other chlorinated hydrocarbons or chlorofluorocarbons emitted from the high-temperature combustion change cannot be eliminated.
According to more recent findings (Abfallwirtschaftsjournal 2/1990 No. 4), a secondary, catalytically initiated dioxin formation takes place particularly place in the waste heat system when the range of 350.degree. to 300.degree. C. is traversed, in addition to the primary dioxin formation in the high-temperature stage of a waste incinerating plant. It has been suggested to inhibit dioxin formation here by injecting specific chemicals. In addition to the difficult operation sequence, in particular in view of the temperature profile, the primary dioxin formation is, however, not prevented by this, since this share is already present in the flue waste gas.
Thus, a decisive disadvantage of most known waste incinerating plants and combustion processes which could not be eliminated so far consists in that, in view of the temperature level and the homogeneity they temperature field in the combustion zones of the do not have the prerequisites for a complete thermal destruction of the polychlorinated hydrocarbons.
It has also already been suggested to dispose of waste products by means of a chemically reactive steam plasma without forming pollutants. However, this process is not suited for the detoxification of large gas flows such as fresh flue gas flows from waste incinerating plants, which have low pollutant concentrations, since its use is impossible for energy reasons (heating up of very large gas flows) and is also ineffective in terms of process technology, because the chemically reactive influence of the steam plasma on the pollutants could not be achieved in a gas flow consisting almost completely of flue gas. Further reasons, e.g. that a plasmatron/plasma reactor combination could not be operated with such large flue gas flows, oppose to the use of this process in the present case of application.
Moreover, it is also already known to carry out a final flue gas purification behind the special waste combustion by means of the dioxins, furans and polycyclic hydrocarbons to activated coke (Abfallwirtschaftsjournal 2/1990, No. 4, page 173). However, this process certainly requires additional expensive process steps and expensive materials and leads to the production of a highly concentrated activated coke, whose disposal is again difficult and which may form a new, great environmental pollution.